Dark Reckoning is a health stealing debuff that also appears to explode in an aoe after a number of seconds. This spell can target both players and pets, so pets should be set on passive and moved away from the group if they receive this debuff.

There is also an Aura of Darkness, a constant aoe, 2625 to 3375 on every player within 40 yards, so no way to avoid it. It lasts until cancelled. The damage is constant, and instant cast so not interruptable. It is however shadow damage so an aura or buff helps to mitigate it. Melee heavy groups will wish they had more casters to use, since the constant aoe is a healing burden, and it is easier to just use ranged plus the tanks.

There is some indication of a third ability called Soul Feast, but little information so far on what it does.